In a conventional writing instrument with a pre-sharpened lead pencil element, such as that shown in U.S. Pat. No. 3,338,215, a number of pre-sharpened lead cartridges or writing units are contained in a tubular holder or casing to form the pencil body. At its rear end, the casing is provided with clicking means to prevent the foremost writing unit from retracting into the casing during use.
These cartridges are then connected in the casing with the front end of one unit received in a recess at the rear end of the next adjacent cartridge.
This arrangement has the disadvantage that when the pencil is in use, the foremost writing unit is supported only at the end where the unit projects out of the casing. Consequently, the foremost writing unit is unstable and wobbly, which causes discomfort in writing.
Another disadvantage with this type of pencil is the difficulty encountered in inserting the last writing unit into the locking means at the rear end of the casing whenever the replacement of a fresh cartridge is required.
Furthermore, because it is difficult to control the inner diameter of the locking means at both ends of the pencil during manufacturing, especially when plastic material is used to form a casing, the inner diameter of both locking means is always either larger or smaller than the outer diameter of the cartridge to be fitted. A larger diameter of the locking means will generally result in the writing unit slipping out from the casing.
Still another disadvantage of this type of pencil is that, if one of the writing units or cartridges is accidentally lost, the remaining writing units contained in the tubular casing will not be able to retain the cartridge assembly, and the entire pencil becomes unusable.
In another conventional writing instrument with a pre-sharpened lead pencil element, shown in Austrian Pat. No. 68637, a number of pre-sharpened leads are contained in an inner front barrel and a push stem is supported by a fixed inner rear barrel, inside which a movable barrel is provided for pushing the push stem so as to project one writing unit each time out of the casing. In addition, a guide ring securely fitted in the casing for the guidance of the movable barrel, spring, supporting union and the pressing and are still particularly needed to perform its functions. One of the disadvantages of this type of pencil is that many parts are required to form a pencil body. This complicated construction will always be accompanied by manufacturing difficulties thus increasing the cost of the pencil. Another disadvantage of this type of pencil is that each writing unit is cylindrically fitted with the casing, between which a critical tolerance is necessary, otherwise, the writing unit will fail in use.
The present invention thus generally relates to a novel magnetic writing implement and, more particularly, to a pencil adapted to avoid the disadvantages of the pencils of the prior art.